Soft Washing T1-11, Hardiplank, and Other Painted Wood

Did a good amount of digging and could find little information regarding soft-washing painted wood surfaces. Lots on stained or sofit. I am still getting started having only completed a few soft wash jobs on vinyl. In my area of the pacific northwest, the vast majority of homes are painted wood, primarily T1-11 or hardiplank/fiber cement.

What is recommended for painted wood? Use a usual vinyl soft wash solution of 1%? The only post I could find with some information is the one linked below, but I was hoping someone could give their opinion as well. It goes without saying but of course any observations like cracked paint would be discussed with the customer and a test area would be used if necessary.

Continuing the discussion from Soft Washing Painted Wood and Stucco?:

It’s all going to depend on what it’s painted with. Colored and dark paints are really finicky, and unless the clients still have an old can of it, it’s hard to know the pigment makeup. Best you can do is a test-spot on the worst looking side to see how it’ll react. Double the strength you think you’ll need for the wash, and give it plenty of time to react.

Thanks for the reply Jake. So on every house, every case, if it’s painted wood you would require a test section? That’ll be rough to do for every house with dry time, but good to know!

I would do a test spot too but I wouldn’t spray a whole side to find out because that’ll require painting if it lightens it up or leaves spots. I do a test spot on all wood houses. Just keep a small spray bottle filled up with SH. Make it strong so you know for sure if it will react and change the color. If it doesn’t react to 3%-4% you know house wash mix won’t do anything to it. Find an inconspicuous area like behind a bush near the bottom or behind a gas meter and give it a good spritz. This will only take a minute, you won’t have to get all set up, and you’ll know right away if it messes it up. If you go and do in person estimates (I don’t) you can just test then so you don’t have to go back if you can’t wash it. Now, there aren’t any organics you can just use your soap to wash the house. I’m sure you get plenty of organics where you’re at though.


I do the same with painted and aluminum siding. I use my pump up and spray it with 50/50 mix of sh and water. I set up and check to see if it had any effect. I also do a small spot low on the siding on the sunny side of the house. It’s not a guarantee that the siding won’t be affected but it’s pretty safe to say the rest of the house will react the same.